The invention concerns in general the technology of forcing a radio device to operate in a certain way by external means. Especially the invention concerns the problem of subdueing the noticeable operation of mobile terminals in certain parts of a cellular radio system.
In addition to and despite of offering remarkable advantages in the form of mobile communications, radio devices are sources for potential harm ranging from annoyance to serious life hazard. An example of the former is a mobile telephone alarm sounding in the middle of a concert, a theatre show or other event where the audience is expected to remain essentially silent. A life hazard may follow if a radio device emits electromagnetic radiation in an aircraft, near life-critical medical equipment or in the vicinity of electrically triggered explosives. Warning signs or acoustic announcements that ask all users to shut down their radio devices offer only a partial solution to this problem, because they do not prevent absent-minded users or deliberate violators from ignoring the request.
A group of prior art solutions for the problem is previously known from the patent publication number WO 97/22049. The publication contains a thorough description of an electronic device that comprises, among its other features, means for sensing the occurrence of a take-off or landing when used inside an aircraft. The first alternative embodiment is to provide within the electronic device a predetermined number of sensors for detecting movement and acceleration. Another embodiment comprises a separate transmitter inside the aircraft for transmitting, as a response to a command given by an airline employee, a signal that is received by a receiver in the electronic device. In a third embodiment the electronic device comprises also a transmitter for emitting a signal that would notify the aircraft of the presence of the electronic device. A corresponding transmitter in the aircraft would then transmit an inhibit signal to the electronic device during take-offs and landings. In any case, when the electronic device produces a positive observation of a take-off or a landing taking place, it powers down all such functions that could cause dangerous electromagnetic emissions.
Some similar solutions are known from the Finnish patent application number 972813. It describes a mobile telephone that comprises, in addition to its conventional functional blocks, a separate radio or infrared receiver for receiving inhibit signals from a local transmitter. Whenever the separate receiver receives an inhibit signal at a power level that exceeds a certain threshold, it powers down the transmitter part of the conventional transceiver and set the mobile telephone into silent mode, where no audible alarms or keypad tones will be emitted.
The drawbacks of the mentioned prior art solutions are related to the excessive need of devices and components that must be added to the existing systems to make the operational restrictions work. A manufacturer of radio devices may be very reluctant to increase production costs by adding into his product features that actually weaken the level of service that the user of the radio device will get. An inhibit signal transmitted in the form of infrared radiation is also vulnerable to the infrared receiver in the electronic device being dirty, covered or adversely directed so that the inhibit signal will not be received correctly.
It is an object of the present invention to provide an economically attractive and functionally reliable solution to the problem of restricted area operation.
The objects of the invention are achieved by using the conventional functional blocks of mobile terminals for implementing the restricted operation mode.
It is characteristic to a system for restricting the operation of radio devices according to the invention that for imposing restrictions to the operation of the mobile terminals on at least one isolated, geographically defined restricted area it comprises a certain first base station arranged to transmit, similary to other general information, information about the nature of the restrictions applicable on said area to the mobile stations.
Additionally the invention concerns a method, comprising as its characteristic features the steps of
providing a radio interface for the mobile terminal through a number of base stations,
using said radio interface for general broadcasts on a common downlink channel and
transmitting, similar to said general broadcasts, information about the nature of the restrictions applicable on said area.
According to the invention, restrictions will be placed to the operation of mobile terminals of a cellular radio system in a certain region. The invention provides two ways of defining these so-called xe2x80x9crestricted areasxe2x80x9d; said two ways may be used either independently or as complementing each other. The first way is to use, within the restricted area, a predetermined number of beacon base stations. A beacon is a base station that is able to communicate information to the terminals like all other base stations in the cellular radio system but allows only restricted operation to the mobile terminals within its cell. The second way of defining a restricted area is to use coordinates that mark off a certain two- or three dimensional physical region. It is also possible to add a further dimension to the definition by giving time coordinates. The base stations of the cellular radio system that are physically close to the restricted area will most advantageously transmit the coordinates of the restricted area to all mobile terminals, although this is not mandatory to the invention. A separate terminal location system will provide location information for each terminal, and when the location information indicates that the mobile terminal is within the restricted area, operational restrictions will apply.
The two ways of defining a restricted area may be combined so that the coordinates of the beacon base stations and the radii of their cells will be used as the coordinates defining the restricted areas, whereby it will be possible to announce the existence and location of the restricted area(s) to a mobile terminal even if it is not yet entering a restricted area.
The restrictions that will be placed to the operation of the mobile terminals may vary according to need. We will categorize them into two classes, which are
restrictions affecting the emission of electromagnetic radiation and
restrictions affecting the human-noticeable operation of the terminal.
A major part of the former class is formed by ways of limiting the normal operation of the transmitter part in the mobile terminal""s radio transceiver, i.e. limiting or inhibiting uplink radio transmissions. The latter class will consist mainly of restrictions to acoustic emissions such as ringing sounds and keypad tones.
A terminal which is about to enter or entering a restricted area may inform its user and/or the network about the situation. During restricted operation the terminal and/or the network may execute procedures aiming at minimizing the loss of information due to the restrictions; examples of such procedures are the direction of incoming calls to a voice mail service and the reception and storage of paging messages in the terminal for indicating to the user the time of an attempted call and the possible identification of the caller.